I tested an upgrade from Ubuntu 16.04 to Ubuntu 18.04 today using the dist-upgrader from -proposed (manually downloaded and extracted b/c you can't use do-release -p and -d) before the upgrade I had installed an updated version of snapd so /var/cache/apt/archives was 14 MB. After the upgrade it was still 14 MB indicating that the debs downloaded for the upgrade had been removed from disk.
I tested an upgrade from Ubuntu 16.04 to Ubuntu 18.04 today using the dist-upgrader from -proposed (manually downloaded and extracted b/c you can't use do-release -p and -d) before the upgrade I had installed an updated version of snapd so /var/cache/ apt/archives was 14 MB. After the upgrade it was still 14 MB indicating that the debs downloaded for the upgrade had been removed from disk.
bdmurray@ clean-xenial- amd64:~ /u-r-u$ du -sh /var/cache/ apt/archives apt/archives/ partial' : Permission denied apt/archives clean-xenial- amd64:~ /u-r-u$ ls -lh /var/cache/ apt/archives/ 2.34.2_ amd64.deb 34.2_amd64. deb core-launcher_ 2.34.2_ amd64.deb
du: cannot read directory '/var/cache/
14M /var/cache/
bdmurray@
total 14M
-rw-r----- 1 root root 0 Jul 19 2016 lock
drwx------ 2 _apt root 4.0K Aug 6 11:22 partial
-rw-r--r-- 1 root root 1.7K Jul 19 03:58 snap-confine_
-rw-r--r-- 1 root root 14M Jul 19 03:58 snapd_2.
-rw-r--r-- 1 root root 1.6K Jul 19 03:58 ubuntu-
Setting to verification-done.